1. Field of the Invention
The present invention relates to an image forming apparatus such as a printer or a copying machine for producing a copy and a management system therefor which can prevent illegal copy.
2. Description of the Prior Art
Recently, copying machines are developed and used widely. Then, infringement of copy right and illegal copies of secret documents become problems to be solved. However, it is impossible for analog copying machines to check an original document precisely. Further, for a document including a partial copy, it is quite impossible to manage hard copies after the second generation of copy of the original document.
There have been proposed many apparatuses and methods in order to prevent the leakage of secret documents by copying. For example, if a copying apparatus detects a phrase registered beforehand such as xe2x80x9cDO NOT COPYxe2x80x9d or xe2x80x9cCONFIDENTIALxe2x80x9d, the copy operation is stopped (Japanese Patent laid open Publication 266,759/1990). However, an illegal copy is easy by copying a document by shading the registered phrases. Therefore, if a copy is once obtained by shading the registered phrases, it cannot be prevented to be leaked. It is also disclosed that an illegal copy can be detected by using information on the characteristics of a document on the image of the whole document such as the position and the number of a specified character such as xe2x80x9cuxe2x80x9d. However, this requires a memory of large capacity to store all characters.
In order to prevent illegal copies of paper moneys and valuable securities with a copying apparatus, it is proposed to store a pattern of characteristics of an image for prohibiting copying and to stop the copying operation for an image of a document including such a characteristic (Japanese Patent laid open Publication 52,384/1990). If a whole document image is stored as a characteristic pattern, this copying machine can deal with even a case where a part of the characteristic pattern is shaded. However, in order to store all characteristic information for a secret document, a memory of large capacity is needed also in this case. Further, it is difficult to detect all information in correspondence to copying operation.
It is also proposed that a password is needed for a copying apparatus (Japanese Patent laid open Publications 120,753/1990 and 120,561/1991). However, it is a problem that a password is needed even for a non-secret document.
On the other hand, in order to trace the origin of leakage of a secret document, it is proposed to add information to a part of a copy of a document (Japanese Patent laid open Publication 111,161/1990). That is, information such as recognition data of a copying apparatus, copy data and copy time are expressed as bar codes, and the bar codes are added in a part of a copy. However, this approach is ineffective if the bar codes to be added in a copy is shaded or if bar codes added for another non-secret document is stuck to a copy to re-generate the copy.
It is also proposed to change a font for a secret document from that of an ordinary document in order to recognize a copy of secret document from the others (U.S. Pat. No. 4,837,737). Then, even if the copies of secret documents are edited or changed, a copy of a secret document can be recognized. However, this approach is ineffective if a document includes only drawings, graphs or the like.
The synthesis of character data with an image data in the image processing with a computer is proposed (Yasuhiro Nakamura and Kineo Matsui, xe2x80x9cA unified coding method of image and text data using three-level micro-patternsxe2x80x9d, Gazou Densi Gakkaishi Vol. 17, No.1 (1988) 3-9). In the image processing wherein the sum of the dots in a small area of nxc3x97n dots is used as a density of a dot to be displayed, a pattern corresponds with a density, and text data are synthesized with an image data by using the patterns. However, if this approach is applied to a copying machine, it is impossible to recognize the patterns in a hard copy. Therefore, this approach cannot be applied to trace the leakage of secret documents.
An object of the present invention is to provide an image forming apparatus which can prevent an illegal copy effectively.
Another object of the present invention is to provide an image forming apparatus which can detect an illegal copy effectively.
A further object of the present invention is to provide a copy management system which can manage copies to detect and to prevent an illegal copy.
In one aspect of the present invention, an additional data useful for the management of copies of a document produced by an image forming apparatus is embedded in a hard copy of the document. The additional data is embedded in an inherent image of a document as discrete dots arranged in a prescribed format. Preferably, the size of each of said discrete dots is not so large as to be recognized easily with naked eyes. The additional data can be embedded in unit of blocks. Further, the density of the discrete dots is selected to be different from the density adjacent to the discrete dots. The image data for embedding an additional data can be obtained by reading a document, or by receiving data sent from a computer or read from a floppy disk,
In a second aspect of the present invention, an additional data embedded in a hard copy as mentioned above can be extracted from an image on the hard copy. That is, the image data includes an additional data embedded in the inherent image as discrete dots arranged in a prescribed format, and it can be recognized and extracted. Further, an image forming means for producing a copy according to the image data can be controlled according to the extracted additional data. For example, if the additional data means that the source of the hard copy is a secret document, the copying is allowed only for a legitimate user.
In a third aspect of the present invention, an additional data as mentioned above is generated for each copy according to the extracted additional data. Then, the generated additional data is embedded in a hard copy. Thus, each copy can be identified.
In a fourth aspect of the present invention, a management means stores the additional data generated for each copy produced in a plurality of printers and the like. Thus, copies of various sources can be managed systematically and illegal copies can be traced easily. If the additional data extracted from an image in a hard copy is not consistent with the additional data already stored, the printing of the hard copy may be prohibited.
In a fifth aspect of the present invention, a document such as a book includes a transmitter which transmits an additional data of the document wireless. The additional data received is used to control the image forming means.
An advantage of the present invention is that the situation of copying can be grasped according to the additional data. For example, the total copy number from the same original document can be counted easily.
Another advantage of the present invention is that an additional data for managing copies can be embedded in an image of a document without deteriorating the reproduced image substantially.
A still another advantage of the present invention is that an illegal copy such as a copy of a secret document by an non-legitimate user can be detected according to the additional data extracted from the copy.
A further advantage of the present invention is that the leakage of a secret document can be prevented.
A still further advantage of the present invention is that an illegal copy can be detected even if a document is edited.